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The developmental toxicity of endosulfan was examined in the anuran Bombina orientalis embryos. Survival rates of embryos following 50 microM endosulfan treatment was significantly lower than vehicle control at 96 h onward. When the embryos develop to the tail fin circulation stage, embryonic survival was significantly decreased by 10 microM endosulfan treatment. Surviving embryos showed various developmental abnormalities including tail dysplasia at 50 microM. By hampering the embryonic development endosulfan may cause the decline in the natural populations of this frog species breeding on farmland and in the surrounding aquatic environment.

Molinate, a thiocarbamate chemical is a slightly to moderately toxic herbicide in EPA (Environmental Protection Agency) toxicity class III, and is a registered as a General Use Pesticide (GUP). Bombina orientalis is one of the most common amphibians in the world and comprise a large proportion of their total number in Korea. B. orientalis spawns in the rice fields at spring when the massive application of agricultural chemicals occurs. In the present study, we examined the effects of molinate on embryonic survival and developmental abnormality in B. orientalis embryos. The difference in survival rate between vehicle control and molinate treated embryos was not observed until the blastula stage. The first statistically significant decrease in embryonic survival was observed at mouth open stage following exposure to 100 microM molinate (46.8% vs. 81.1% in control). When the embryos develop to tadpole stage survival was significantly decreased at 50 microM molinate (35.9% vs. 68.9% in control), suggesting that the lowest observed effective dose (LOED) for systemic toxicity in B. orientalis embryos is 50 microM. In survived embryos molinate exposure produced several types of severe developmental abnormalities in order of frequency with bent trunk, neurula with yolk plug, bent tail, tail dysplasia, ventral blister, eye dysplasia, thick-set body and cephalic dysplasia. This suggests that molinate targets multiple events in embryonic and larval development in this frog species. Together this suggested that molinate was detrimental for survival and development following zygotic transcription after midblastula transition in B. orientalis embryos.